The allied campaign of 1709 had begun in mid June after a late start owing to the unusually harsh winter preceding it.

Unable to bring the French army under Marshal Villars to battle, owing to strong French defensive lines and the Marshal's orders from Versailles not to risk battle, the Duke of Marlborough has concentrated instead on taking the fortresses of Tournai and Ypres.

Tournai had fallen after an unusually long siege of almost seventy days, by which time it is early September, and rather than run the risk of disease spreading in his army in the poorly draining land around Ypres, Marlborough instead moves eastwards towards the lesser fortress of Mons, hoping by taking it to outflank the French defensive lines in the west.

Villars moves after him, under new orders from Louis XIV to prevent the fall of Mons at all costs – effectively an order for the aggressive Marshal to give battle.

After several complicated maneuvers, the two armies face each other across the gap of Malplaquet, southwest of Mons.

The allied army, mainly consisting of Dutch and Austrian troops, but also with considerable British and Prussian contingents, is led by Marlborough and Prince Eugene of Savoy, while the French and a contingent of Bavarians are commanded by Villars and Marshal Boufflers.

Boufflers is officially Villars' superior but is voluntarily serving under him.

The allies have about eighty-six thousand troops and one hundred guns and the French have about seventy-five thousand and eighty guns.

They are encamped within cannon range of each other near what is now the France/Belgium border.

At 9.00 AM on September 11, the Austrians attack with the support of Prussian and Danish troops under the command of Count Albrecht Konrad Finck von Finckenstein, pushing the French left wing back into the forest behind them.

The Dutch under command of John William Friso, Prince of Orange, on the Allied left wing, attack the French right flank half an hour later, and succeed with heavy casualties in distracting Boufflers enough so that he cannot come to Villars' aid.

Villars is able to regroup his forces, but Marlborough and Eugène attack again, assisted by the advance of a detachment under General Withers advancing on the French left flank, forcing Villars to divert forces from his center to confront them.

At around 1.00 PM, Villars is badly wounded by a musket ball that smashes his knee, and command passes to Boufflers.

The decisive final attack is made on the now weakened French center by British infantry under the command of the Earl of Orkney, which manages to occupy the French line of redans.

This enables the Allied cavalry to advance through this line and confront the French cavalry behind it.

A fierce cavalry battle now ensues, in which Boufflers personally leads the elite troops of the Maison du Roi.

He manages no less than six times to drive the Allied cavalry back upon the redans, but every time the French cavalry in its turn is driven back by British infantry fire.

Boufflers, realizing by 3.00 PM, that the battle cannot be won, finally orders a retreat, which is made in good order.

The Allies have suffered so many casualties in their attack that they cannot pursue him.

By this time, they have lost over twenty-one thousand men, almost twice as many as the French.

By the norms of warfare of the era, the battle is an allied victory, because the French withdraw at the end of the day's fighting, and leave Marlborough's army in possession of the battlefield, but with double the casualties.

In contrast with the Duke's previous victories, however, the French army has been able to withdraw in good order and relatively intact, and remains a potent threat to further allied operations.